1. Field of the Invention
The present invention generally relates to overdrive and gamma systems, and more particularly to overdrive compensations/updates adaptable to a dynamic analog gamma generator.
2. Description of the Prior Art
Due to the liquid crystal capacitor of the liquid crystal molecules in a liquid crystal display (LCD), the liquid crystal molecules require a period of time to reach target orientations, and therefore the change of brightness of pixel usually lags behind the change of voltage difference employed between the pixel electrode and the common electrode. In order to increase the response time of the liquid crystal molecules, an overdrive (OD) technique is usually employed. A conventional overdrive system is typically implemented by an overdrive lookup table (OD LUT) as exemplified and simplified in the following Table 1.
TABLE 1prev.curr.08162432 0 00000 81385421629211697245638322418328660534032
The overdrive lookup table outputs an overdrive gray code to the source driver based on a previous-frame gray code and a current-frame gray code. In Table 1, the horizontal axis represents the previous-frame gray code, and the vertical axis represents the current-frame gray code. The retrieved gray code according to the previous-frame gray code and the current-frame gray code is the output gray code to be provided to the source driver. For example, if the previous-frame gray code is “0” and the current-frame gray code is “8”, the code “13” is thus retrieved as the output gray code to the source driver.
The LCD typically includes a gamma reference voltage generator for the purpose of correcting the non-linear perception of human eyes. FIG. 1A shows a conventional gamma reference voltage generator (gamma generator, in short) which uses a voltage divider made of serially connected resistors 10. In modern image processing applications (such as contrast adjustment), the reference voltages generated by the gamma generator are dynamically adjusted. FIG. 1B shows, for example, an adaptive analog gamma reference voltage generator 12 disclosed in “Contrast Enhancement in Liquid Crystal Displays by Adaptive Modification of Analog Gamma Reference Voltages” by Seung-Woo Lee, IEICE Trans. Electron., Vol. E90-C, No. 11, pp. 2083-2087, November 2007, the disclosure of which is hereby incorporated by reference.
Whenever the reference voltage generated by the adaptive gamma generator 12 is adjusted from a curve A to another curve B as shown in FIG. 1C, the relationship between the output voltage level to the (data) gray code is accordingly changed. On the other hand, the relationship between the output gray code and the input gray code in the overdrive lookup table (Table 1), however, does not change accordingly. That is, the gray level in the overdrive lookup table has not adaptively adjusted as it should have in accordance with the adaptive adjustment in the adaptive gamma generator 12.
For the reason that the conventional overdrive lookup table could not adaptively keep up with the adaptive adjustment of the gamma generator, a need has arisen to propose a novel overdrive compensation or updating scheme adaptable to a dynamic or adaptive analog gamma generator.